1. Field of the Invention
The present invention relates to a treatment apparatus using a gas, such as a reaction treatment apparatus used in the manufacturing of semiconductor devices and liquid crystal drive circuit substrates, for treating an object such as a wafer substrate with a reaction gas and, more particularly, to a shield mechanism for the protection of a portion of the apparatus which is otherwise liable to be corroded (hereinafter called "corrodible portion") in an atmosphere contained in a treatment space of this type of apparatus.
2. Description of the Related Art
Processes for manufacturing semiconductor devices and liquid crystal drive circuit substrates generally employ a heat treatment apparatus which supplies a reaction gas to a heating reaction tube in order to carry out thin-film forming, impurity diffusion, oxidation, etching, and the like.
The above heat treatment apparatus typically comprises a treatment space, a heating tube surrounding the treatment space, a heating coil wound around the heating tube, and a heat-insulating layer wrapped around the heating coil. The treatment space is generally a hollow cylinder made of quartz and having an opening at one end, and the heating tube is made of silicon carbide or the like. In operation, a wafer boat containing a plurality of semiconductor wafers is inserted into the treatment space, through the opening, and then a predetermined reaction gas such as SiH.sub.4, O.sub.2, B.sub.2 H.sub.6, or PH.sub.3 is introduced into the treatment space. In advance of this, an electrical current is supplied to the heating coil, whereby the coil heats the heating tube, which in turn heats the treatment space uniformly to a predetermined temperature ranging from several hundred degrees centigrade to one thousand and several hundred degrees centigrade. As a result, the semiconductor wafers are heat-treated, and either a film is formed on the wafers or an impurity is diffused thereinto.
Heat-treatment apparatuses of this type are classified into vertical-type and horizontal-type apparatuses. Since the vertical-type heat-treatment apparatus occupies less floor space than the horizontal-type apparatus, it is therefore more popular.
Published Examined Japanese Patent Application No. 62-14223 discloses a vertical heat-treatment apparatus in which the reaction tube contains a table for supporting a wafer coat, a loading/unloading mechanism for mounting the boat on the table and demounting it from the table, and a rotary mechanism for rotating the boat, mounted on the table, about the vertical axis. The loading/unloading mechanism and the rotary mechanism are both interlocked with the table. A shaft is connected at one end to the motor of the rotary mechanism, and at its other end extends into the reaction tube, through a hole formed therein, and is connected to the wafer boat. Although the reaction tube is penetrated by the shaft, the tube is hermetically sealed by a seal member fitted in the hole and containing a magnetic fluid and having a bearing for supporting the shaft.
However, use of the seal member gives rise to the following problem: To epitaxially grow a silicon layer on the wafers, silane tetrachloride (SiCl.sub.4), trichlorosilane (SiHC.sub.3), or the like is made to react with hydrogen (H.sub.2). During this reaction, hydrogen chloride (HCl) is produced, and reacts with the magnetic fluid contained in the seal member, generating a gas which hinders the desired reaction taking place on the wafers. Moreover, not only does the hydrogen chloride corrode the seal member, but also the bearing, jeopardizing the hermetic seal of the reaction tube and the smooth rotation of the shaft. Consequently, the production yield achieved by the vertical heat-treatment apparatus is relatively low.